Theory: The Butcher and the Box
Okay, here's my take on this - they were all tweakers! We find out he was dealing drugs, which 95% of the time, means also doing them.
The reason she took so long to leave (even after she found out her kids were beaten) was because he was her hookup. Free drugs, don't need to work.
I don't buy for a second that she didn't know he was beating the kids. How did she not notice those marks on her children's back and legs? Oh that's right, because she was spun out and not paying attention.
So she FINALLY leaves when she finds out he's been raping her daughter. But he knows where she lives and probably even has a key since he was able to get inside and bug the house. She invited him over to give him the tapes, so she certainly didn't cut ties with him.
I'm sorry, but fuck this bitch. She let him back over even after what he did?
Why? Because he gives her drugs. That's the only thing that makes sense.
The crazy tweaker notebooks filled with psychotic abuse fantasy stories? Yeah, they were high AF.
Also, the ex-wife reminds me of Aunt Lydia from Handmaid's Tale